Much of bulk return mail is processed with at least some manual handling, especially when it contains orders. Once cut open, the envelopes are generally emptied by hand; and information from their contents is keyboarded, optically scanned, or otherwise entered into a computer. The required steps of opening the envelopes, separating their contents, and entering relevant data are expensive and time consuming. Also, data entry is subject to error, especially when information printed on the envelopes must be linked to information from their contents.
Outgoing bulk mail is also subject to sorting and other processing errors that are difficult to detect; because once sealed, their contents are concealed from view. For example, inserts containing confidential information can be placed in the wrong envelopes addressed to persons who become privy to private information of others. Many different approaches have been used to see through the envelopes and read their contents without opening them but problems plague each.
U.S. Pat. No. 5,522,921 to Custer proposes use of x-rays for reading envelope contents that are printed with special x-ray opaque materials. The x-rays penetrate the envelopes and their contents except where blocked by the special materials. A resulting shadow pattern is detected by an x-ray reading device. However, the special materials add expense and limit printing options, and the x-rays pose health risks that are difficult to justify for these purposes.
U.S. Pat. No. 5,288,994 to Berson proposes using infrared light in a similar manner to read the contents of sealed envelopes. A light source directs a beam of the infrared light through the envelopes to an optical detector that records a shadow pattern caused by different absorption characteristics between conventional inks and the paper on which they are printed. However, such filled envelopes make poor optical elements for transmitting images, even for transmissions in the infrared spectrum. Paper does not transmit the infrared images very efficiently. Irregularities in the surfaces, spacing, layering, and materials of the envelopes and their contents cause significant aberrations that can greatly diminish resolution of the images. Also, overlays of printed material on the envelopes and their contents are difficult to separate, and printed backgrounds can reduce contrast.
Except for differences in wavelength, these prior approaches are analogous to shining a flashlight through one side of an envelope in the hope of reading darker printed matter through the envelope's opposite side. X-rays penetrate paper very easily but are dangerous and require special materials to stop them. Near infrared wavelengths transmit poorly through paper, and their images are subject to aberration from optical inconsistencies and to obscuration from printed overlays or backgrounds.
U.S. Pat. No. 5,811,792 by two of the present co-inventors, Verschuur and Mitchell, Jr., proposes a combination of microwave heating and infrared viewing to access the contents of sealed envelopes. Microwave energy differentially heats conductive or dielectric patterns in the contents, and infrared detectors record thermal images of the patterns conducted to the envelopes' surfaces.
U.S. Pat. No. 5,621,200 to Irwin, Jr. et al. discloses an electronic validation system for scratch-off lottery tickets. A conductive ink containing a pattern of resistors is printed as a portion of the scratch-off material or underlying play indicia. Capacitors couple the printed resistor circuits to an electronic verification machine to verify electronic signature patterns of the resistor circuits. The electronic signatures are comparable to predetermined standards, but they do not contain information encoded in conventional formats that can be read as alphanumeric characters. Also, each ticket must be tested one at a time at a predetermined position within the verification machine.
U.S. Pat. No. 3,519,802 to Cinque et al. discloses an early attempt at authenticating credit cards with internally encoded data. Conductive plates are arranged in a pattern; and their presence, absence, or proximate orientation is detected by a capacitance sensor. However, the detection system requires the conductive plates to be bent into two offset planes that complicate manufacture and are not readily applicable to thinner substrates such as sheet materials normally enclosed by envelopes.
U.S. Pat. No. 4,591,189 to Holmen et al. discloses a more recent example of a credit card verification system in which a light-transmitting authenticating layer is sandwiched between two anti-reflective film layers. The authenticating layer is preferably vacuum deposited, such as by sputtering, but can also be formed by a printed layer of conductive ink. The impedance, conductance, or capacitance of the authenticating layer can be detected, though capacitance is not recommended for detecting discrete areas of the authenticating layer. Beyond authentication, the conductive layer does not contain any useful information.
U.S. patent application Ser. No. 09/059,985 by Verschuur, Mitchell, Jr., and Leordeanu describes a capacitive method and apparatus for reading barcode printed on inserts and hidden inside sealed envelopes. Changes in a measurement of capacitive coupling between two electrodes in the presence of the barcode is interpreted to distinguish different barcode patterns. This application is hereby incorporated by reference.
A number of factors can affect such capacitive coupling measurements including wobble of the envelopes past the electrodes, vibration of the envelope transport, different numbers or thicknesses of dielectric layers separating the barcode from the electrodes, variations in the position or angular orientation of the barcode, and overcoupling effects between adjacent bars of the barcode.